1. Field of the Invention
The invention refers to a method in a microtome, especially an ultramicrotome, in which a knife edge which can be oriented around its longitudinal axis, is used to cut sections from a specimen by making the specimen pass downwardly over the knife edge, thereby making it the distance between the knife edge and the specimen before cutting extremely narrow without the specimen touching the knife.
2. Prior Art
Within microtomy, especially ultramicrotomy, there is a strong requirement for the monitoring and controlling the approach of the cutting knife to the specimen from which the sections are to be cut. The knives used generally consist of glass or diamond and the knife edges are extremely sharp and, therefore, are easy to damage if the knife, when approaching the specimen comes into contact with the specimen or if the first cut is too thick. On the other hand, if due to insufficient sensitivity of the control of the distance between the knife and the specimen surface, one is forced to feed the knife and the specimen in very small steps at a long distance between the knife and the specimen the process will take an unreasonable amount of time. According to an earlier known method, the approach between the knife and the specimen block is carried out in such a way that the slit between the knife and the specimen block is lit up from below by a separate lamp located in the knife holder under the specimen block and the knife. According to another method described in Swedish Pat. No. 7504111-1, the knife is lit up from below via a mirror. This latter method can, however, only be used for glass knives. In the former method the location of the light source under the knife holder leads to thermal disturbances and furthermore, a light beam which is too strong and too broad is obtained. This gives a dazzling effect which is especially disturbing in the subsequent cutting procedure in which so-called diffused light is used. In order to reduce the thermal disturbances and to decrease the dazzling effect, the lamp could be replaced by a fiber optic arrangement placed on the knife holder. The drawback is, however, that one has to take away the fiber cable before the cutting is started which easily gives rise to mechanical disturbances of the knife holder. Or, one has to let the cable remain during the cutting, which easily gives rise to mechanical tensions between the knife stage and the base plate and which, furthermore, contributes to the transfer of vibrations to the knife holder.